Internal combustion (IC) engines normally are designed to operate on a single energy-dense liquid fossil fuel, such as gasoline or diesel. Under typical conditions, in a first step the designated liquid fuel is injected into a chamber comprising a reciprocating piston. The fuel is mixed with an oxidizer, typically oxygen supplied as air. In a second step, the piston moves to compress the mixture. In a third step, the compressed mixture is either spark ignited (SI) or compression ignited (CI) depending upon the liquid fuel employed, whereupon combustion occurs to produce an expanding mixture of gaseous combustion products. The gaseous products produce a force on the piston, which moves the piston over a distance. Mechanical energy derived from the moving piston is converted into useful mechanical or electrical work. After maximum expansion, the piston retracts as the gases exit the chamber; and thereafter the process is repeated many times.
In one type of IC engine combustion is intermittent, as exemplified in familiar two-stroke and four stroke engines. Such engines find utility in motive applications and are the predominant power supply for cars, motorcycles, boats and small gasoline-powered engines, such as lawn mowers. Such engines also find utility in electrical power generators, which are useful, for example, in logistics and rescue operations (i.e., field operations) and for temporary power generation during disruptions in a power grid. Small portable generators of about 1 to 3 kilowatts electric (1-3 kWe) output are especially useful in logistics and rescue operations. In another type of IC engine, combustion is continuous. Such engines find utility in large-scale stationary power applications, such as gas turbine power plants, and larger more powerful motive applications, such as jet engines and rocket engines. The present invention is particularly directed to the intermittent IC engine and its use in mobile and stationary applications of a smaller, more portable scale as noted above.
Spark-ignited internal combustion (SI-IC) engines are designed for operation on a high octane fuel having an octane number typically greater than 80, for example, gasoline. For power generation under logistics and field conditions, gasoline is currently considered an undesirable fuel. For one reason, gasoline has a higher volatility and lower flash point as compared with lower octane liquid distillate fuels, such as JP-8 and diesel. Thus, providing a supply train for gasoline is more problematical than providing a supply train for distillate fuels. Moreover, providing multiple fuel trains is undesirable. Accordingly, it would be desirable to operate all power generation sources, both stationary and motive including those under field conditions, on one fuel, namely, a distillate fuel such as diesel or JP-8. As is well understood in the art, a spark-ignited gasoline engine is not designed for operation on a low octane distillate fuel.
Distillate fuels, such as JP-8, have a low octane number; for example, diesel has an octane number between about 15 and 25. Engines designed for operation on low octane fuel employ compression ignition (CI) and typically are large, heavy, and thick-walled to withstand compression pressures. Additionally, combustion of distillate fuels, such as diesel, generates soot and other unacceptable emissions. Operation of a diesel engine at reduced power is quite inefficient resulting in a condition called “wet stacking”, a term used to describe deposition of unburned fuel inside the diesel engine exhaust system. An engine running in this condition generates considerable soot that without frequent cleaning can lead to catastrophic failure of the engine. Thus, the CI internal combustion engine operating on diesel fuel is not a suitable engine for logistics operations where small, light-weight, lower power (e.g., 0.3-3.0 kWe) features are needed. In view of the above, it would be desirable to redesign a SI internal combustion engine, originally designed for operation on a high octane fuel like gasoline, to operate on a low octane fuel, such as diesel or JP-8.
In one application, lightweight portable generator sets (hereinafter “gensets”), which produce about 1-3 kWe power, are commercially ubiquitous; however, these gensets employ a SI internal combustion engine and operate solely on high octane gasoline. Adapting these gensets to operate on low octane diesel or JP-8 would significantly alter power dynamics and offer advantages under field conditions.
U.S. Pat. No. 4,131,095 discloses an internal combustion engine operating on a reformed gas produced through reformation of “an ordinary liquid fuel typified by gasoline.” The internal combustion engine is disclosed to comprise four combustion chambers, wherein the first combustion chamber is constructed to act as a reformer to convert the ordinary liquid fuel into a mixture of hydrogen and carbon monoxide and wherein the three remaining chambers are constructed to receive reformate and the ordinary liquid fuel. The engine is taught to operate solely on gasoline reformate, solely on liquid gasoline, or on a mixture of reformate and liquid gasoline.
U.S. Pat. No. 7,174,861 discloses a combined gasoline and hydrogen fueling system for gasoline-powered internal combustion engines, including a catalytic reformer for producing gaseous reformate from gasoline. The patent teaches that the reformate from the reformer is swept by air into the intake manifold of the cold engine, where it is mixed with intake air and then drawn into the cylinders and ignited conventionally to start the engine before the engine is transitioned to operation on gasoline.
Among other references disclosing the adaptation of an internal combustion engine with a fuel reformer are U.S. Pat. No. 4,033,133, and US 2014/0109844, and the following non-patent literature publications: F. Y. Hagos, A. R. A. Aziz, and S. A. Sulaiman, “Trends of Syngas as a Fuel in Internal Combustion Engines”, Advances in Mechanical Engineering, Hindawi Publishing Corporation, Vol. 2014 (2014), Article ID 401587, 10 pp.; and S. Brusca, V. Chido, A. Galvagno, R. Lanzafame, and A. M. C. Garrano, “Analysis of Reforming Gas Combustion in Internal Combustion Engine”, Energy Procedia, 45 (2014), 899-908.
Some prior art related to modifying an internal combustion engine with a fuel reformer tends not to disclose details of the fuel reformer or discloses inherently large, bulky reformer apparatuses. These reformers can exhibit unacceptable efficiency and can produce coke and degradation in hydrogen yield within a short time frame, rendering such apparatuses unacceptable for onboard motive or portable stationary applications. Other prior art attempts to achieve distillate fueling of an IC engine through distillate fuel vaporization, which does not actually change the fuel's low octane number and thus does not overcome the low octane issue. This latter approach suffers from durability and reliability issues inherent to vaporization in field use.
In view of the above, the intermittent spark-ignited internal combustion engine designed to operate on high octane fuel, such as gasoline, would benefit from design modifications that allow for multi-fuel operation. Such modifications should desirably involve no substantive redesign or reconfiguration of the spark-ignited internal combustion engine itself. Rather, the SI internal combustion engine should be simply retrofit with additional components that provide the desired novel functionality. It would be beneficial for a gasoline-fueled SI internal combustion engine to operate fully on a low octane distillate fuel, namely diesel or JP-8, so as to simplify fuel supply trains and to provide light-weight, portable engines and generators, preferably of 0.3 to 3.0 kWe output, suitable for a variety of logistics and field operations. Such modifications should desirably result in a spark-ignited internal combustion engine that meets existing emissions standards.